R. MOLLE (syn Azalea mollis), from Japan (1867), is a dwarf, deciduous species of neat growth, with flame-coloured flowers. It is very hardy, and a desirable acquisition to any collection of small-growing shrubs.
R. OCCIDENTALE (syn Azalea occidentalis), Western Azalea, is valuable in that the flowers are produced later than those of almost any other species. These are white, blotched with yellow at the base of the upper petals; and being produced when the leaves are almost fully developed, have a very pleasing effect, particularly as they are borne in great quantity, and show well above the foliage. This is a Californian species that has been found further west of the Rocky Mountains than any other member of Ihe family.
R. PARVIFOLIUM.—Baiacul, 1877. This is a pleasing and interesting species, with small deep-green ovate leaves, and clusters of white flowers, margined with rose. It is of dwarf and neat growth, and well suited for planting on the rock garden.
R. PONTICUM.—Pontic Rhododendron, or Rose Bay. Asia Minor, 1763. This is the commonest species in cultivation, and although originally a native of the district by the Black or Pontic Sea, is now naturalised in many parts of Europe. It is the hardiest and least exacting of the large flowered species, and is generally employed as a stock on which to graft the less hardy kinds. Flowers, in the typical species, pale purplish-violet and spotted. There is a great number of varieties, including white, pink, scarlet, and double-flowering.
R. PONTICUM AZALEOIDES (syn R. ponticum deciduum), a hybrid between R. ponticum and a hardy Azalea, is a sub-evergreen form, with a compact habit of growth, and bearing loose heads of fragrant lavender-and-white flowers. It is quite hardy at Kew.
R. RACEMOSUM.—Central China, 1880. A neat little species, of dwarf, compact growth, from the Yunnan district of China. The flowers are pale pink edged with a deeper tint, about an inch across, and borne in terminal and axillary clusters. It has stood unharmed for several years in southern England, so may be regarded as at least fairly hardy. Its neat dwarf growth, and flowering as it does when hardly a foot high, renders it a choice subject for the Alpine garden.
R. RHODORA (syn Rhodora canadensis).—North America, 1767. In general aspect this shrub resembles an Azalea, but it comes into flower long even before R. molle. Being deciduous, and producing its pretty purplish sweet-scented flowers in early spring, gives to the plant a particular value for gardening purposes, clumps of the shrub being most effective at the very time when flowers are at their scarcest. It thrives well in any peaty soil, and is quite hardy.
R. VISCOSUM (syn Azalea viscosa).—Clammy Azalea, or Swamp Honeysuckle. North America, 1734. This is one of the hardiest, most floriferous, and easily managed of the family. The white or rose and deliciously fragrant flowers are produced in great abundance, and impart when at their best quite a charm to the shrub. It delights in rather moist, peaty soil, and grows all the stronger and flowers all the more freely when surrounded by rising ground or tall trees at considerable distance away. The variety R. viscosum glaucum has leaves paler than those of the species; and R. viscosum nitidum, of dwarf, compact growth, has leaves deep green on both sides.
R. WILSONI, a cross between R. ciliatum and R. glaucum, is of remarkably neat growth, and worthy of cultivation where small-sized kinds are a desideratum.
The following Himalayan species have been found to thrive well in the warmer parts of England, and in close proximity to the sea;—R. argenteum, R. arboreum, R. Aucklandii, R. barbatum, R. ciliatum, R. campanulatum, R. cinnabarinum, R. Campbelli, R. compylocarpum, R. eximium, R. Fortunei, R. Falconeri, R. glaucum, R. Hodgsoni, R. lanatum, R. niveum, R. Roylei, R. Thompsoni, and R. Wallichii.